The use of jet propulsion devices for marine craft is well known technology. Jet propulsion has many advantages over the simple propeller, particularly in terms of maneuverability, and jet propulsion energy consumption is much more efficient. However, widespread acceptance of jet propulsion for marine craft has not occurred because of certain common problems associated with marine jet propulsion. For example, marine jet propulsion poses significant design problems because of uncertain performance over a wide range of speeds, water depth, sea conditions, etc.
Excess water pickup at the jet propulsion unit inlet may cause balling, i.e., excess water pressure between the hull and the inlet because the unit is not able to intake a sufficient volume of water during craft maneuvers or poor sea conditions. Balling induces a high drag characteristic adversely affecting the propulsive efficiency. Cavitation is another common problem. Cavitation represents an uneven load on the impeller. Cavitation can be produced by excessive radial acceleration of the fluid, excess swirl and turbulence of the fluid column, and unintentional partial vaporization of the fluid throughput associated with a vacuum produced by impeller action.
Accordingly, it would be desirable to design a jet propulsion unit for marine vessels where each feature synergistically work together to provide for a constant column of water even at high output and where the water throughput is neither turbulent nor swirling in order to eliminate cavitation effects. Furthermore, the unit should have maximum flexibility to cope with the entire speed range of the marine vessel and varying loading on the unit without producing the above-mentioned balling and cavitation effects.
Finally, the unit ought to be efficient at preventing intake of foreign matter, yet have provided therefor a quick means for manually cleaning the intake if fouling occurs.
U.S. Pat. No. 3,187,708 to Fox discloses a housing unit for boats that supplants the gear box propeller and rudder structure of the usual power boat arrangements The jet unit is entirely outside of the boat hull and the construction of the housing is arranged so that the outside shell of the unit is very smooth and has a minimum of projections thereon which might engage and snag on objects in the water. The forward and reverse mechanism consists of a balance deflector damper within the discharge nozzle.
U.S. Pat. No. 3,192,715 to Engel, et al. discloses a steering device for a jet propelled water craft. The steering device is provided with a control system.
U.S. Pat. No. 3,302,605 to Kuether discloses a rudder jet propulsion apparatus for water craft having a water inlet in the hull, an impeller connected to a motor means, and an outlet in the form of a nozzle. The intake is provided with a rotary weed cutting device that is operated by the drive means for the impeller. A clutch may be used for optionally coupling and uncoupling the weed cutting device from the drive means.
U.S. Pat. No. 3,598,808 to Shields discloses a marine propulsion device providing a semi-submerged super-cavitating propeller rotating coaxially with water jet-producing impellers mounted on the same shaft.
U.S. Pat. No. 3,620,019 to Munte discloses a jet propulsion drive having an upright housing at the rear end of a water craft and a cross-sectional outline resembling a symmetrical trapezium. The narrowest side of the housing faces oppositely the extended movement of the water craft and a pair of side walls extend from the narrow side in the direction of intended movement. Inlet means are provided for admitting water into the housing and outlet means are in the narrow side for expelling water from the housing. An expeller vane is mounted in the housing for pivotal movement immediate the respective side walls about an upright axis extending through the housing in the region of the outlet means.
U.S. Pat. No. 3,624,737 to Keller discloses an underwater jet propulsion nozzle including means for injecting air into the jet stream issuing from the nozzle to give increased thrust when stationary or at low speeds. The nozzle is mounted for swiveling movement on a fixed jet pipe and the plane of the swivel joint is inclined downwards in the direction of forward motion.
U.S. Pat. No. 3,842,787 to Giacosa discloses a water jet impeller unit of the type comprising a duct along which water forced by means of a motor driven propeller housed in the duct in which there is provided a deflector nozzle at the downstream of the duct which is pivoted about a substantially vertical hinge axis. The deflector nozzle has a main nozzle outlet facing rearwardly and two subsidiary nozzle outlets facing forwardly and diverging outwardly, the subsidiary nozzle outlets are variable in size by virtue of their cooperation with the size of the duct so that as the nozzle turns about its hinges, one of the subsidiary outlets becomes enlarged while the other diminishes. The nozzle also carries a baffle at the main outlet thereof which is moveable between an open position where it allows water to flow out through the main nozzle outlet, and a closed position where it forces water to flow through the subsidiary outlets to provide a reverse thrust which can be adjusted by inclination of the nozzle about its hinged axis.
U.S. Pat. No. 4,652,244 to Drury discloses a stream of water is caused to move through a duct carried within the hull of a water craft and discharge as a jet in a direction which is nondirectional to the craft. The jet is redirected, as by a plate or nozzle to impart movement to the craft in a selected direction.
U.S. Pat. No. 4,643,685 to Nishida discloses a water jet propelled craft equipped in the rear section of the craft with a water jet pump driven by an engine. The rear end of a nozzle of the water jet pump has an outlet for exhaust gas from the engine.
U.S. Pat. No. 4,718,870 to Watts discloses a marine propulsion water jet system which includes a fluid flow amplifier by which a high velocity principal water flow is injected into a slower velocity secondary water flow to form a water jet. The fluid flow amplifier includes an adjustable orifice to which the principal water flow the orifice is automatically adjusted in order to maintain a relatively constant water jet velocity.
U.S. Pat. No. 4,600,394 to Dritz discloses a marine propulsion unit which is designed for intensifying the thrust obtained by an impeller such as a propeller for standard outboard or inboard/outboard marine propulsion systems. The unit design incorporates an axial flow or screw type impeller operating within a housing which terminates in an area of reduced cross-sectional which augments the thrust delivered by the impeller. The impeller blades virtually abut the inner circumference and fill the cross-sectional area of the housing near the inlet port.
U.S. Pat. No. 3,776,173 to Horwitz discloses a propulsion system for a boat that not only provides forward movement and directional control, but also provides means for controlling the attitude of the boat. The control system uses a jet nozzle mounting structure that permits the nozzle to pivot in a horizontal direction and/or in a vertical direction
Australian Patent Application 24907/88, filed Nov. 1, 1988 and opened to public inspection May 11, 1989, discloses a marine propulsion unit comprising a housing with a variable inlet induction, first set of vanes downstream of said induction, a propeller/impeller, a second set of vanes downstream of said propeller and a convergent discharge housing downstream of said second set of vanes. The use of a variable inlet orifice induction is said to reduce choking within the induction, and therefore cavitation and drag. The marine propulsion unit may be used with either outboard or sterndrive power trains.
U.S. Pat. No. 3,589,325 to Tattersil discloses a marine craft fitted with a water jet propulsion unit having a rudder disposed adjacent the outlet of the unit so as to influence the direction taken by water discharged by the outlet. The rudder is pivotable about an axis passing through the plane of its surface and the outlet of the unit.
U.S. Pat. Nos. 3,782,320 to Groves and 3,788,265 to Moore disclose a control assembly for a boat having a water jet propulsion system in which the jet is discharged successively through a discharge conduit and nozzle. The nozzle is moveable with respect to the conduit and is provided with a moveable bucket whereby the nozzle and bucket are moveable into different positions of adjustment to control the jet, and thus control the steering, fore and aft movements and the desired planing of the boat.
U.S. Pat. No. 4,432,736 to Parramore discloses a steering mechanism for a water jet propelled craft having a rotatable propulsion nozzle. The mechanism comprises controls which rotate the nozzle via a differential gear box. The steering control is operative to rotate a gear box input shaft via a worm and pinion reduction gear and the reversal control is operable to rotate the cage. The nozzle is connected to a gear box output of the shaft.
U.S. Pat. No. 3,993,015 to Klepacz et al. discloses a hydraulic propulsion for water craft involving the forming of a parallel-sided, open-ended inlet intake tunnel with a recessed intake screen which directs the incoming water into a single or multistaged cylindrical axial pump having multivaned matched impellers and straighteners for driving the flow into an unobstructed acceleration chamber which converges the flow and discharges it as a jet through a cylindrical opening with controls thereat to propel and steer the craft.